Method for separating two elements and a device therefor

ABSTRACT

A process and device for separating two semi-conductor substrate wafers along an interface. The process includes forming a cavity, and initiating separation by applying force to the interface through the cavity. The device utilizes fluid or gas, and pressure chambers, to subject adherent faces of the interface to at least one of chemical or mechanical action.

TECHNICAL FIELD

The present invention relates to a process for separating two elementsadhering one to the other by means of adherent faces, with thisseparation being able to be obtained under the action of a fluid and/ora mechanical element allowing the separation to be initiated locally. Italso relates to a device for implementation of this process.

The invention applies in particular to the field of micro-electronics inorder to separate two plates adhering one to the other. It is ofparticular interest in handling thin, fragile and very flexible plates.

STATE OF PRIOR TECHNIQUE

Document FR-A-2 752 332 discloses a process for separation of a supportplate by the insertion, at the bonding interface, of a quite flexibleseparator element so as not to scratch the surfaces. This separatorelement consists of several parts allowing minimum optical sighting,during the operation to open the interface, to be compatible with anindustrial goal. This process was developed for plates bonded by meansof attractive forces.

The article entitled “Bonding of silicon wafers forsilicon-on-insulator” by W. P. MASZARA et al., published in the reviewJ. Appl. Phys. 64 (10), 15 Nov. 1988, pages 4943-4950, relates to themeasurement of bonding energy by the method of the blade inserted at theinterface of two elements adhering one to the other. For a given bondingenergy, the thicker the blade, the further the opening wave propagatesfrom the opening point at the bonding interface. Similarly, the greaterthe bonding energy, the less the separation wave propagates for a givenblade thickness.

To apply a separation process as described in document FR-A-2 752 332,it is advantageous if the surface energy is low and the separatorelement is thick. A separation wave may thus be propagated over asignificant length compared to the diameter of the plates forseparation.

However, use of a thick separator element may lead to a fracture of oneof the plates due to the curvature radius being too low. In addition, ithas been shown that the greater the bonding energy, the more the bladeor the separator element must be inserted gently in the interface toprevent the risk of fracture of the plates, relaxation of the openingstresses being made possible through a sufficiently slow opening.

In addition, in the case of a structure with several interfaces, theopening may be propagated from one interface to another, associated, forexample, with a lower bonding energy.

It is also known that the bonding energy between two elements increaseswhen a thermal treatment is applied. On this subject one may refer tothe article by C. MALEVILLE et al., published in the reviewElectrochemical Society Proceedings Volume 97-36, pages 46-55. As an aexample, silicon plates the surfaces of which have been made hydrophilicare bonded to one another. A bonding energy greater than 1 J/m² isobtained for bondings followed by thermal treatment at 1000° C. Thus,for silicon plates 525 μm thick (typical thickness of plates of 100 mmdiameter), a blade 600 μm thick succeeds in causing an opening of thebonding interface over a length of around 3 cm or less. This length ofopening is insufficient to separate the plates. It is then necessary tointroduce a thicker separator to propagate this opening. This causes areduction of the flexibility of the separator elements and involves therisks mentioned above.

Inserting a blade is not the only method enabling two elements bonded toone another to constitute a structure to be separated. Document WO 98/52216 describes a process for controlled cleavage of a substrate throughthe introduction of particles, originating, for example, from a steamsource, from a side of the structure where the interface ends. However,this technique can be used only to separate stacks in which a zone haspreviously been embrittled, for example by ion implantation. Theseparation interface can then only be the embrittled zone. U.S. Pat. No.5,863,375 discloses the separation of two plates bonded to one anotherto constitute a structure. Separation is obtained under the effect of ajet of liquid directed on the plane of the interface to a face of thestructure where the interface ends.

Moreover, the faces of the plates for separation may have received,before being bonded, one or more deposits of thin films. In this case itis not possible to use the teaching of U.S. Pat. No. 5,863,375. Theseparation liquid jet also acts on deposited films.

As there is no precise location of the bonding interface, the separationmay occur in one of the deposited layers if the adherence energy of afilm to its plate is less than the adherence energy of the bondinginterface between the two plates. This technique is also very expense interms of the consumption of fluid used, since a large quantity of thisfluid does not act on the bonding interface.

These known techniques for separation using a jet of particles or a jetof liquid replacing a separating blade reveal other problems. A firstproblem relates to the precise location of the opening interface. Otherproblems are related to the fact that to apply the opening techniqueseasily the bonding interface must not be too resistant taking account ofthe various thermal treatments which can be applied.

Traditionally, the bonding energy may be controlled by preparing thesurfaces to modify their hydrophilic character or their roughness. Onthis subject, one may refer, for example, to the document “influence ofsurface characteristics on direct wafer bonding” by O. Rayssac andcoll., 2^(nd) international conference on materials formicro-electronics, 14/15 Sep. 1998, ION Communications Ltd.

Document EP-A-0 703 609 discloses a process for transferring a thinsemiconducting layer from a support substrate to a target substrate,taking advantage of the fact that the bonding energy between the layerand the support substrate is less than the bonding energy between thelayer and the target substrate. When a pulling and/or shearing and/ortorsion force is applied to the structure, the separation occurs betweenthe layer and the support substrate, thus causing the layer to betransferred.

This process must, as above, take account of the possible problem ofresistance of the bonding interface.

In addition, the thin layer is bonded to the support substrate in orderto undergo a number of processes including, for example, one or moredeposits of thin films the adherence energy of which may prove to belower than the bonding energy of the substrates to each other. Inparticular, methods of separation based on traction, shearing ortorsion, applied globally to the substrates, may not be used.

ACCOUNT OF THE INVENTION

The invention has been designed to remedy the disadvantages reportedabove.

To this end, the invention relates more specifically to a process forseparating two elements of a structure containing both elements put inadherent contact with one another by respective adherent faces and withat least one interface.

Before adherent contact is accomplished, the process involves at leastone cavity being made. The cavity is made in at least one of theelements, ending respectively at the interface, to allow separators topass into the cavity. The process also comprises, during separation, theexercise of a force, in a localised manner in the interface, through theapplication of the said separators to initiate the separation of the twoelements from the interface and to continue it, if applicable, untilcomplete separation of the two elements.

The separators may include, among other things, means exerting amechanical action and/or fluid pressure and/or exerting a chemicalaction on at least one of the adherent faces at the interface.

Thus, the force applied to the interface must be understood as resultingfrom a mechanical and/or fluid pressure and/or chemical action.

The cavities may be obtained by engraving. They may be made on theperiphery or in a more central region of the elements. In particularthey may be distributed across all or part of an interface of adherencebetween the elements, so as to control propagation of the separationopening. The cavities may also extend as far as an interface separatefrom that formed by the elements' adherence faces, inside one of theelements.

If several interfaces are used for the separators, the cavities may bearranged so as to initiate the separation at a given location of theinterfaces.

When the separators include means exerting a fluid pressure in theinterface zone, and when this fluid is liquid, these separators mayinclude microwaves or impulse excitation of the liquid fluid.

The two elements may be put into adherence with one another with anadherence energy which varies according to the various regions of theadherence interface so as to initiate the separation at a given locationof the interface.

In addition, the separators may be such that the separation of the twoelements in the interface occurs at one or more locations in asimultaneous or sequential manner.

The invention also relates to a device for separating two elements of astructure, adhering to one another by adherence faces at least one ofwhich has cavities in an interface zone, so as to be able to subject atleast one of the adherence faces to the influence of a fluid andpossibly to a mechanical action, with the device comprising an enclosurewith at least a first chamber called a high-pressure chamber able toreceive the fluid, and a second chamber, called a low-pressure chamber,the enclosure being formed so as to receive both the adherent elementsof the structure such that the cavities communicate with the highpressure chamber.

This device may also include means forming a stop to a deformationconsidered excessive of one and/or the other element of the structure ontheir separation.

The enclosure may, preferably, be fitted with at least one jointarranged between an element of the structure and the wall of theenclosure to separate the high-pressure chamber from the low-pressurechamber.

The invention also relates to a handle for transferring objects such as,for example, electronic chips. The handle has an adherence face withcavities in at least one interface zone, to which objects may adhere,and the handle also has means of access to the interface zones toseparate objects from them. The objects are of various dimensions, froma few microns to several tens of centimetres for example.

The means of access are, for example, channels or any other type ofdepression or perforation made in the adherence face.

The handle may contain a plate one face of which constitutes theadherence face, with the plate being pierced with penetrating holesending in the interface zones and constituting the said means of accessto the interface zones. The penetrating holes may be holes allowing atool for separating objects to be passed through.

The means of access to the interface zones preferably allow a fluidpressure to be applied to the objects.

A fourth goal of the invention relates to a process for localisedtransfer of objects made on the surface of a first substrate, with anadherence face, where the process comprises the following stages (inthis order or in another order):

putting the adherence face of one or more object in adherent contactwith the adherence face of a transfer handle as described above.

possibly, thinning of the first substrate from the free face of thisfirst substrate,

placing into adherent contact of at least one of the said objects with areceiving substrate, and

separation of the said object from the handle using the means of accessto the interface zone,

The process may be completed by the separation of the transfer handle,which may contain objects which are not yet transferred, and of thereceiving substrate which contains the transferred objects.

If the objects are not separated from one another, i.e. clipped beforethe placing into adherent contact with the receiving substrate, theprocess may also include a stage of clipping of objects so as to allowtheir individual transfer.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and other advantages andfeatures will appear on reading the following description, given as anon-limiting example, accompanied by the annexed drawings, among which:

FIG. 1A represents, as a transverse section, a first possibility forembodiment of a device according to the invention intended forseparating two elements adhering to one another,

FIGS. 1B and 1C are partial schematic sections illustrating possiblevariants for embodiment of the device of FIG. A1.

FIG. 2 represents, seen as a transverse section, a second possibleembodiment of a device according to the invention intended forseparating two elements adhering to one another,

FIGS. 3A to 3C illustrate the conduct of the process of separating twoelements adhering to one another, according to the invention,

FIGS. 4A to 4D illustrate application of the process according to theinvention for obtaining a semi-conductive membrane, the main faces ofwhich receive treatments using micro-electronics techniques,

FIGS. 5A to 5F illustrate the transfer of an electronic chip from afirst substrate to a receiving substrate using the process according tothe present invention,

FIGS. 6 to 12 illustrate schematically various possibilities for formingan adherence face of an element of a structure, for use in separation inaccordance with the invention,

FIG. 13 is a transverse section of a structure formed from two elementsand with two interface zones for a separation in accordance with theinvention,

FIG. 14 is a view from above of an adherence face of an element of aspecific structure for use in a separation,

FIG. 15 is a schematic section of a structure including the element ofFIG. 14.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention allows the separation of two elements the adherencesurfaces of which may be bonded by means such as, for example, glues(polymers, epoxy, etc.) or bonded by molecular adherence. The inventionapplies particularly well to the case in which these elements are platesand notably if one of these plates is a semi-conductive plate the twoprincipal faces of which may receive a treatment using micro-electronicstechniques.

The idea consists in introducing a means, notably a fluid and/or amechanical tool, around the bonding interface so as to cause an actionallowing all or part of the elements to be separated, offering thechoice of being able to locate the interface zone for separation in thefirst place. A fluid may, for example, be introduced at the interface,using an engraving undertaken prior to the bonding in one of theelements or in both. Tests have shown that an engraving of this kind maybe undertaken without hindering the bonding. To allow the introductionof a fluid, this engraving must communicate with the outside. It may becommunicating at the periphery or through one of the elements. Theseparation may thus be initiated in the vicinity of the engraved zone.

The engraving may be undertake to constitute, for example, a network ofblocks, a network of cavities, whether or not penetrating, or take aspiral shape or a ring shape or a shape in sectors. These variouspossibilities are illustrated by FIGS. 6 to 12 described below.

The fluid may be introduced using an adapter in the cavity made byengraving, or by placing the structure formed from the two bondedelements in an enclosure filled with fluid the pressure of which iscontrolled.

FIG. 1A shows in section a first possibility of embodiment of a deviceaccording to the invention allowing the separation of two elements. Inthe example of the figure, the elements are two circular plates 1 and 2bonded to one another with an interface 3. The device contains a sealedenclosure 4 of cylindrical shape with a lower wall 5 and an upper wall6. Joints, for example toric joints, 7 and 8, are fixed respectively tothe lower wall 5 and upper wall 6 and support the main faces of theplates the device is dimensioned according to the size of plates 1 and 2which are to be separated. The device is connected laterally to a duct 9for conveying fluid, on to which is mounted a valve 10.

When the structure consisting of plates 1 and 2 bonded to each other isinstalled in the device, enclosure 4 is divided into several chambers: achamber 11 called the high-pressure chamber, for receiving the fluidconveyed by duct 9, and two chambers 12 and 13 located respectivelyabove and below the structure for separation, and called low-pressurechambers.

The pressure which the fluid must exert to cause the separation dependson the adherence energy between the plates. In the case of a molecularadherence, the latter is determined in particular by preparing thesurfaces before bonding and also by the thermal treatment(s) undergoneby the structure. To remain within the limit of elastic deformation andnot to deform the plates irremediably, it is possible to alter thedistance between the bonded structure and the inner surface of theenclosure located opposite the plates. Stops 14 and 15 fixed on theinner surface of the enclosure allow the deformations caused in theplates to be limited, and may, favour separation. The initial distancebetween the stop and the corresponding plate depends notably on thethickness of the plate and its nature.

FIG. 1A shows that plate 2 contains a peripheral engraving 16 allowingthe fluid to reach an interface zone 17.

References 18 and 19 designate ducts respectively in communication withthe low-pressure chambers 12 and 13, which can be designed to controlthe pressure of a fluid located in these chambers. Ducts 18 and 19 canbe simple vents, able to be put in communication, for example with theatmospheric pressure. They can also be linked to means for adjusting thepressure of a fluid, for example a gas located in the low-pressurechambers, so as to control the separation precisely. The pressure of thefluid in the low-pressure chambers is, however, maintained at a lowervalue than the pressure of the fluid applied to the high-pressurechamber, to allow separation.

FIG. 1B shows, in a partial manner, and on a larger scale, anotherpossible embodiment of the separation device constituting a variantcompared to FIG. 1A. The identical parts, similar or corresponding tothat of FIG. 1, are identified with the same numerical references andtheir account is not given here.

It is observed in FIG. 1B that joints, for example toric joints, 7 and 8are not fixed on the upper and lower walls of the device but on thelateral walls which are facing the plate's edges.

Joints 7 and 8 rest respectively on the edges of the plates at asufficient distance from the bonding interface so as not to hinderaccess of the pressurised fluid to the peripheral engraving 16 and thusto the interface zone 17.

The action of the fluid on the adherence faces in the interface zone isindicated by arrows. Arrows also indicate the separation of the platespushed back towards the low-pressure chambers 12 and 13.

FIG. 1C also shows, in a partial manner and on a larger scale, yetanother possible embodiment of the separation device, constituting avariant in relation to FIGS. 1A and 1B. The parts identical or similarto those of the previous figures are always indicated with the samereferences.

It is observed in FIG. 1C that the toric joints have been eliminated andreplaced by a lip joint J. Joint provides sealing between the lateralwall of the device and the first and second plates. It also providessealing between the high-pressure chamber 11 and the low-pressurechambers 12 and 13.

A passage P made in joint J allows the pressurised fluid to reach theinterface zone 17 of plates 1 and 2.

FIG. 2 shows yet another possible embodiment of a device according tothe invention allowing the separation of two circular plates 21 and 22bonded one to another with an interface 23. A duct 29 conveying fluid isconnected differently from that of FIG. 1A. It leads to the centre ofthe lower wall 25 of enclosure 24. This device divides enclosure 24 intoa high-pressure chamber 35 and into two low-pressure chambers: chamber31 and chamber 32 and in which plate 21 may be deformed.

FIG. 2 shows that plate 22 has a central penetrating hole 26 allowingthe fluid to reach an interface zone 37. The central hole may bereplaced and/or completed by other holes penetrating the plate (withidentical or different diameters).

FIGS. 3A to 3C illustrate an example of the conduct of the process ofseparation of plates 1 and 2 in FIG. 1. At the start of the operation,the fluid is introduced and starts to exert its action on the walls ofcavity 16 and the interface zone 17 as is shown by the arrows in FIG.3A. FIG. 3B shows an example of the commencement of the separationbetween plates 1 and 2 under the action of the fluid pressure and therole of stops 14 and 15. Plate 1 in this example is deformed more thanplate 2. This example occurs in the case where one fie, plate is finerthan the other. Thus, in the case of power electronic applications, itis possible, thanks to the invention, to produce and manipulatemembranes of several tens of micrometers. FIG. 3C shows plates 1 and 2totally separated.

In the cases represented in FIGS. 1 and 2, plates 1 and 21 are, forexample, elements or membranes in which circuits can be produced whereasplates 2 and 22 are elements reserved for the separation operation.Plates 2 and 22 can be designated under the name transfer handles. Thesehandles are easy to re-use.

The advantage of locating the engraving in the plate used as a handle isthat, in addition to localising the separation of the structurehorizontally, this allows the interface to be localised vertically inthe structure. As indicated above in the state of prior technique, iflayers have been deposited before the plates are bonded (see the layersshown in dot-and-dash lines in FIG. 1) and if these layers have loweradherence than the bonding interface, only this vertical location willallow separation at the bonding interface.

To increase the fluid's effectiveness, it may be advantageous if, inaddition to the pressure action, this fluid is able to exert a chemicalaction in the interface, thus facilitating separation. For an interfacewith a silicon oxide base, a solution formed from HF diluted in watermay be used to control the speed of engraving. If a face for separationmust be preserved (a face treated by micro-electronics techniques, forexample), the part to be preserved may be protected by a stop layer (forexample, polycrystalline silicon) on which the interface oxide isdeposited or formed.

In addition, in the case of a liquid fluid, the separation may befacilitated, for example, through the use of an excitation of themicrowave type, pulse type, etc.

It may be advantageous to prepare one of the adherence faces of at leastone of the plates, partly or wholly, in order that the resulting bondingenergy varies in the plane of the bonding interface. It is possible, forexample, to define a central zone of the interface where the adherencewill be stronger than in the periphery. This energy difference will beexploited to induce the subsequent separation by localising thecommencement of separation in the periphery of the structure. Moregenerally, this technique may be used advantageously to generatelocalised zones where the bonding energy is different to the bondingenergy of the other zones.

FIGS. 4A to 4D illustrate the acquisition of a membrane, for examplemade from a semi-conductive membrane, the main faces of which aretreated using micro-electronics techniques. The goal is to obtain amembrane approximately, for example, 100 μm thick, treated on both facesfrom a standard 4-inch silicon plate 525 μm thick. This plate will haveto be subjected to various operations, for example thermal annealings(typically at 1100° C.), mechanical treatments (polishing, surfacetreatments), chemical treatments (dry or wet engraving), deposits(oxides or metals), and implantations.

These various operations imply manipulations of the membrane, which isproblematic when it is around 100 μm thick or less. The inventionenables this problem to be overcome.

FIG. 4A shows a silicon plate 40 intended to supply a membrane. Theplate is represented with one of its main faces, face 41, which haspreviously undergone treatments using micro-electronic techniques, andwhich has received, for example, an encapsulating oxide layer. The oxidelayer may possibly be polished to give a flat surface.

FIG. 4B shows plate 40 (in a reversed position in relation to FIG. 4A)put in contact by its face 41 with face 48 of a plate 49. Plate 49 isideally a plate of oxidised silicon. Bonding by SiO₂/SiO₂ hydrophilicmolecular adherence may thus be obtained. The bonding energy may becontrolled by varying the more or less hydrophilic or more or less roughnature of the surfaces. It is then possible to undertake operationsusing micro-electronic techniques with the other face, face 42, of plate40, in perfect safety from the mechanical standpoint to obtain finally amembrane treated on both faces.

As indicated above, to obtain the desired molecular adherence, it ispossible to modify the hydrophilic nature and/or roughness usingtraditional techniques. By combining both methods, after annealing at1100° C., it is possible to obtain a bonding energy of around 500 mJ/m²for an SiO₂/SiO₂ structure the surface roughnesses of which aretypically 0.6 nm RMS (root mean square). This value is substantiallyless than that (2 J/m²) obtained for bonding of plates the surfaceroughness of which is around 0.2 nm. With this bonding energy value, theprocess of the invention allows plate 40 to be separated from plate 49and a fine membrane to be obtained finally which has been subjected toat least one treatment on at least one of its faces, with a minimal riskof deterioration.

As yet another example, this technique may be used advantageously togenerate localised zones the bonding energy of which is different fromthe bonding energy of the remainder of the structure. The variation ofthe bonding energy, in different zones, may be obtained by a techniqueusing partial masking of at least one of the surfaces in contact in thebonding. For example, it is possible to generate different surfaceroughnesses in masked and non-masked zones by a chemical attack, a dryengraving, an ion implantation, etc.

The roughness may advantageously be controlled so as to cause the lowestbonding energy in the zone (s) chosen for the commencement ofseparation.

Plate 49 (see FIG. 4B) has an engraved part 47 forming an example of acavity of the recess type, giving access to an interface zone 43 onwhich a fluid pressure may be exerted.

FIG. 4C shows the structure obtained successively by surface treatmentand possibly polishing of plate 40 in order to transform this plate intoa membrane 44.

Free face 45 of membrane 44 can then be treated by micro-electronictechniques. A membrane treated on both faces is obtained (see FIG. 4D),which will be separated from plate 49 in accordance with the invention.

In conceivable treatments it is possible to make deposits of layers orengravings, or even transfer another structure on to the membrane,notably to rigidify it.

For certain applications, for example in optoelectronics, it appears tobe advantageous to be able to associate a chip or optoelectroniccomponent produced, for example, on III-V material with an electroniccircuit produced for example on silicon. In this case, to produce anobject of this kind, one approach consists in transferring the chip madeof III-V material to a whole plate containing the circuits. The transferto a whole plate allows the implementation of technological stagessubsequent to the transfer. As an example, one can mention, among theoperations subsequent to the transfer, those allowing contacts to bemade between, for example, the chip and the circuit. The inventionallows electronic chips to be transferred to whole plates. It has theadvantage that it allows chips to be made thinner.

FIGS. 5A to 5F illustrate the transfer of an electronic chip from afirst substrate to a receiving substrate.

FIG. 5A shows a plate 50 one of the principal faces of which, face 51,has been treated to produce individualised chips 52. The chips may, forexample, be electronic or optoelectronic components. The material ofplate 50 may be of type III-V or GaAs. The area of the chips may be ofaround 250 μm×250 μm.

FIG. 5B shows the joining of plate 50, on the chips side, with a handleplate 53. The joining may be achieved through the bringing into contactwith two plates with bonding by molecular adherence or using anintermediate layer of glue or resin. The joining is realised with acontrolled bonding energy. For example, in the case of molecularbonding, this energy may be chosen by controlling the surface roughnessand/or the hydrophilicity and/or percentage of the area in contact.

If it is desired to transfer chips, handle plate 53 is made such thatholes 54 penetrate it, allowing communication between the two main facesof the handle 53 bonded to the chips. The size and pitch of the holesare appropriate for the size and pitch of the chips. In this example,the pitch of the chips is around 250 μm. The diameter of the holes mustbe appropriate for the pitch and separation technique. If a tool isused, for example, of the injector needle type, it exerts a mechanicalaction. If a separation fluid is used, the dimension of the holes may bevery small, less than or equal to the dimension of the chips. If thechips are larger, for example 500 μm×500 μm, the hole dimension may be,for example, 200 μm. Use of an injector needle is then facilitated.Depending on the dimension of the element to be transferred, one or moreinjector needles may be used. The end of the injector needle may bepointed, flat or conical. The injector needle may also be pierced at theend, for example to convey the fluid. A combination of the fluid and thetool may advantageously be envisaged.

FIG. 5C represents the structure obtained after plate 50 is thinned tothe desired thickness and chips 52 separated one from the other. Ifoptoelectronic components are produced on a GaAs layer, they may bearound 10 μm thick. The separation of the chips may be accomplished byengraving or more simply using a cutting saw.

The thinned structure is brought into contact with a receiving plate 55(see FIG. 5D).

As indicated by an arrow in FIG. 5E, a chip 52 for example may beseparated from the handle plate 53 by means of a tool and/or transferfluid.

When the location of chip 52 for transfer has been prepared on face 56of the receiving plate 55, separating plates 53 and 55 leaves the chipseparated from plate 53 on plate 55, whereas the other chips remain onplate 53.

This process is also of interest for the transfer of thin circuits forsmart card or “disposable ticket” applications.

The present invention has many advantages. Firstly, it can allow bothsides of (for example) a silicon plate to be worked, without any risk ofdeterioration. It is thus possible to treat a first face of a platewhilst protecting the second face, by adherence to a support.Subsequently, the treated face may itself be protected by adherence toanother support while the other face, after separation, is treated inits turn. This invention can also facilitate use of fine plates, alsocalled membranes (less than 300 μm thick for a diameter of 100 mm). Thistype of plate is, for example, found increasingly often inmicro-electronics applications, and also, for example, in powerelectronics. The advantage of this type of plate is that it is possibleto produce structures made from it while limiting, due to theirthinness, problems of thermal heating or leakage current when in use.Conversely, these plates are places where high stresses occur duringuse, due to the thermal treatments they undergo and their thinness. Itis, for example, very risky to put this type of plate in ovens sincethey tend to deform and even in extreme cases to break as a consequenceof the process temperature and stresses generated by the thermaltreatments. In addition, these plates are not always compatible withequipment used in micro-electronics, since the latter are oftencalibrated to receive plates of standard thickness (for example, 525 μmin the case of silicon plates of diameter 100 mm).

Finally, transport and handling of this type of very thin plate must belimited since the risks of breakage are much greater than with standardplates. To remedy these problems, adhering a fine plate to a supportplate allows the fine plate to be rigidified to give it the mechanicalproperties of a thick plate during the various treatment stages. Theplates may be dissociated during or after the process.

All the methods described above may apply both to separation of elementsof large dimensions (for example, whole plates measuring severalcentimetres in diameter) and to the separation of elements of smalldimensions (for example, several tens of microns in width).

FIGS. 6 to 12 described below represent in a very schematic way variousexamples of possible embodiments of the elements of a structure,designed for a separation in accordance with the invention. Theseelements are, for example, handles as described above. In all thesefigures, identical references designate identical or similar parts.

It should be specified that the examples illustrated by FIGS. 6 to 12are not exhaustive and that the various possible ways of formingcavities shown by these figures may be combined with one another.

Reference 100 designates in a general manner the body of the element orhandle which, in the illustrated examples, is represented as a circularplate. A face 102 of the element is also defined, which is the adherenceface, intended to be brought into adherent contact with another bondedelement to form a structure. The two elements of the structure must alsobe separated subsequently along the plane of adherence face 102.

FIG. 6 shows a first example in which cavities 104 a appear as holespenetrating element 100 from side to side to link the adherence face tothe opposite face. The holes may have different diameters and differentshapes. On the adherence face they define an interface zone allowingpreferential localised separation. It is also observed that the holesare made in a more or less central region of the element.

Use of an element 200 in accordance with FIG. 6 was illustratedpreviously in a reference to FIG. 2.

FIG. 7 shows an element 100 with a single cavity 104 b, which isnon-penetrating, in the form of a recess made in the periphery of theelement. Cavity 104 bcorresponds to recess 16 of plate 2 represented inFIGS. 1A to 1C.

FIG. 8 shows an element 100 with an adherence face in which broadchannels 104 c are engraved so as to surround and limit islands 108. Thechannels 104 c allow a pressurised fluid to be applied, but alsoconstitute cavities in the sense of the invention.

FIG. 9 shows an element 100 with an adherence face 102 in which severalnon-penetrating cavities 104 d are made to form a network of cavities.The cavities are linked together by channels 104 e which lead to theperiphery of element 100. The channels 104 e also constitute means ofaccess to the interface zone containing the cavities 104 d.

FIG. 10 shows an element 100 the adherence face 102 of which is dividedinto sectors by channels 104 eextending like spokes. The sectors maythemselves be crossed by channels 104 f in a diagonal intersectingpattern.

In an alternative embodiment, represented in FIG. 11, channels may alsotake the form of concentric circular channels 104 g, communicating by aradial channel 104 h.

In yet another possibility, represented in FIG. 12, a circular,spiral-shaped channel 104 i may extend from the centre to the peripheryof the adherence face 102.

Channels 104 e, 104 f, 104 g, 104 h and 104 i of FIGS. 10 to 12 allowaccess of a fluid and/or of a separation tool but also constitutecavities in the sense of the invention. They thus define interface zonesallowing privileged localised separation.

The interface zone is determined in a general manner by the positioningand/or distribution of the channels on the element's adherence face.

This distribution also allows the element's adherence with a bondedelement, and their subsequent separation, to be controlled precisely. Azone with a high density of channels allows easier separation than azone with a lower density of channels.

As an example, with a spiral-shaped channel, as represented in FIG. 12,the ease of separation depends on the distance between the spires. Theseparation thus tends to be initiated in the centre of the element andto be propagated in a more or less concentric manner towards theperiphery.

This is also the case with the examples of FIGS. 10 and 11.

FIG. 13 shows a structure 200 formed from a first element 201 and asecond element 202.

The two elements are made to form a single piece by their adherencefaces, which thus define a first interface 217.

The first element 201 has undergone ion implantation leading to theformation, at a shallow depth, of an embrittled zone forming a secondinterface 227, in the sense of the invention.

The embrittled zone extends in a manner more or less parallel to thesurface of the first element, i.e. in a manner more or less parallel toits adherence face, thus delimiting a thin surface layer 206 in it.

Emerging cavities 204 are engraved in the first element and extendthrough the thin surface layer 206 before emerging at the secondinterface 227.

In the example of FIG. 13, the bonding force being exerted between thefirst and second elements, i.e. between their adherence faces, is higherthan the bonding force of the second interface 227. The bonding force ofthe second interface is understood here as the force which must beovercome to cause separation in the embrittled zone.

When a fluid is applied through the cavities 204, the structure in FIG.13 will undergo separation, and more specifically separation at thesecond interface.

FIG. 14 shows an adherence face of an element 301 of a structure 300.The latter is designed for the selective transfer of different parts 310of this element 300.

The parts identified with reference 310 are surrounded with cavities 304which are partitioned by walls 305 of the first element.

The cavities enable the different parts 310 to be delimited and extendas far as a buried interface, in the form of an embrittled zone asdescribed above.

FIG. 15 shows in section element 301, which forms a single piece withelement 302, to which the parts 310 must be transferred.

It may be observed that fluid accesses 314 enable the cavities 304 ofthe first element to be supplied selectively, and these cavitiessurround some of the parts 310. This enables them to be separated in thesecond interface 327 and to be selectively transferred to the secondelement 302.

To this end, it should be specified that only some parts 310 may be madea single piece with the second element 302 at the first interface 317.

Once again in this case, the adherence forces at the first interface 317are greater than those at the second interface 327, i.e. greater thanthe forces which must be overcome to detach the parts 310 from element301.

What is claimed is:
 1. A process for separating two semi-conductorsubstrate wafers alone an interface including all points of contactbetween the wafers, both wafers bonded to one another at adherent facesof the interface, the process comprising: forming at least one cavity inat least one of the wafers, the cavity providing access of separationmeans to at least one predetermined zone of the interface; initiatingseparation of the wafers along the interface by applying the separationmeans to the predetermined zone; and continuing separation of the wafersalong the interface, by applying the separation means to thepredetermined zone and to separated portions of the interface, until adesired degree of separation is achieved, wherein points of entry to thecavity are not located solely at an edge surface of the wafers.
 2. Theprocess of claim 1, in which the separation of the two wafers is inducedin more than one predetermined zone, in a simultaneous or sequentialmanner.
 3. The process of claim 1, wherein the separation means containsmeans for exerting a mechanical action at the interface.
 4. The processof claim 1, wherein the separation means contains means for exerting achemical action on at least one of the wafers at the interface.
 5. Theprocess of claim 1, wherein the cavity is obtained, in whole or in part,by engraving.
 6. The process of claim 1, in which the cavity is made ata periphery of at least one of the wafers and provides access of theseparation means to the the adherent faces.
 7. The process of claim 1,wherein the cavity is made in an inner region of at least one of thewafers and does not provide access of the separation means to theadherent faces.
 8. The process of claim 7, wherein the separation meanscontains a liquid, the process further comprising using microwaves toexcite the liquid of the separation means.
 9. The process of claim 1,wherein the cavity penetrates through at least one wafer from side toside.
 10. The process of claim 1, wherein several predetermined zonesare planned and are arranged so as to initiate the separation atdetermined locations of the interface.
 11. The process of claim 1,wherein the two wafers adhere to one another with a different adherenceenergy in different regions of the adherent faces, so as to initiateseparation at a determined location of the adherent faces.
 12. Theprocess of claim 1, for separating two wafers having a first interfaceformed at the adherent faces and a second interface interface in whichthe separation of the wafers is induced at one of the first and secondinterfaces.
 13. The process of claim 12, wherein a bonding energy of thesecond interface is lower than a bonding energy of the first interface,and wherein the separation of the wafers is induced in the secondinterface.
 14. The process of claim 12, in which, before the two wafersare brought into contact, an embrittled zone is formed in at least oneof the two wafers at the second interface.
 15. The process of claim 14,in which the embrittled zone is formed using an implantation techniqueor using a layer adherence technique.
 16. The process of claim 15, inwhich the embrittled zone is formed at a shallow depth in one of thewafers such that the second interface delimits a thin layer in the wafercontaining the embrittled zone.
 17. The process of claim 1, wherein thewafers comprise a first wafer and a second wafer, the first wafer beingat most 100 micrometers thick and the second wafer being used as ahandle for the first wafer.
 18. The process of claim 1, wherein thecavity is formed in the second wafer.
 19. The process of claim 1,wherein the cavity is formed before the wafers are bonded to oneanother.
 20. A device for separating two semi-conductor substrate wafersalong an interface including all points of contact between the wafers,both wafers bonded to one another at adherent faces of the interface, atleast one wafer including a cavity extending to at least one of theadherent faces, points of entry to the cavity not being located solelyat an edge surface of the wafers, the device comprising: fluid or gasfor subjecting the at least one of the adherent faces to at least one ofa chemical or mechanical action; an enclosure with at least onehigh-pressure chamber configured to receive the fluid or gas; and atleast one low-pressure chamber, wherein the enclosure is formed so as toreceive the two wafers such that the cavity communicates with thehigh-pressure chamber.
 21. The device of claim 20, wherein the holdingmeans comprises at least one joint arranged between one of the wafersand a wall of the enclosure.
 22. The device of claim 21, in which atleast one joint is arranged between a main face of at least one of thewafers in a form of a plate and a wall of the enclosure facing the mainface.
 23. The device of claim 21, in which at least one joint isarranged between an edge of at least one of the wafers in a form of aplate and a wall of the enclosure facing the edge.
 24. The device ofclaim 20, wherein the wafers comprise a first wafer and a second wafer,the first wafer being at most 100 micrometers thick and the second waferbeing used as a handle for the first wafer.
 25. The device of claim 20,wherein the cavity is formed in the second wafer.
 26. The device ofclaim 20, wherein the cavity is formed before the wafers are bonded toone another.
 27. A process for separation of first and second wafers,the two wafers bonded by adherent faces of an interface including allpoints of contact between the first and second wafers, the second waferincluding at least one cavity formed in an interface portion of thesecond wafer so as to extend onto the interface and to face an interfaceportion of the first wafer, the process comprising: inserting separationmeans into the cavity, the separation means comprising a liquid or a gasand inducing a higher pressure within the cavity; inducing a lowerpressure within a chamber bounded, in part, by at least one of the twowafers; and preventing excessive deformation of at least one of the twowafers, by providing a stopper within the chamber having the lowerpressure.
 28. The process of claim 27, in which the separation of thetwo wafers is induced in one or more of the interface portions, in asimultaneous or sequential manner.
 29. The process of claim 27, whereinthe separation means further comprises means for exerting a mechanicalaction at the interface.
 30. The process of claim 27, wherein theseparation means further comprises means for exerting a chemical actionon at least one of the wafers at the interface.
 31. The process of claim27, wherein the cavity is obtained, in whole or in part, by engraving.32. The process of claim 27, in which the cavity is made at a peripheryof at least one of the wafers and permits access of the separation meansto the adherent faces.
 33. The process of claim 27, wherein the cavityis made in an inner region of at least one of the wafers and does notpermit access of the separation means to the adherent faces.
 34. Theprocess of claim 33, wherein the separation means contains a liquid, theprocess further comprising using microwaves to excite the liquid of theseparation means.
 35. The process of claim 27, wherein the cavitypenetrates through at least one wafer from side to side.
 36. The processof claim 27, wherein several cavities are planned and are arranged so asto initiate the separation at determined locations of the interface. 37.The process of claim 27, wherein the two wafers adhere to one anotherwith a different adherence energy in different regions of the adherentfaces, so as to initiate separation at a determined location of theadherent faces.
 38. The process of claim 27, for separating two wafershaving at least a first interface portion formed at the adherent facesand at least one second interface portion, in which the separation ofthe wafers is induced at one of the first and second interface portions.39. The process of claim 38, wherein a bonding energy in the secondinterface portion is lower than a bonding energy of the first interfaceportion, and wherein the separation of the wafers is induced in thesecond interface portion.
 40. The process of claim 38, in which, beforethe two wafers are brought into contact, an embrittled zone is formed inat least one of the two wafers at the second interface portion.
 41. Theprocess of claim 40, in which the embrittled zone is formed using animplantation technique or using a layer adherence technique.
 42. Theprocess of claim 41, in which the embrittled zone is formed at a shallowdepth in one of the wafers such that the second interface portiondelimits a thin layer in the wafer containing the embrittled zone.